1. Field of the Invention
The present invention relates to a method for detecting the angular position of a rotor in a brushless electric motor. In particular, a motor of the type in which the emission of a polarity signal of the back electromotive force (Bemf) by a detection circuitry associated with the motor is provided.
More specifically, the method is aimed at improving the detection of the instantaneous position of the rotor in a brushless motor through the detection of the zero-crossing signal, known as “zero-crossing”, of the back electromotive force (Bemf) produced by the motor itself.
This method can be used in all applications using this type of motor: e.g. Floppy and Hard Disk drive, DVD, CD and Tape drive.
2. Description of the Related Art
As is well-known in this specific field of application, it is common practice to refer to the Bemf signal and to “zero crossing” or “ZC” for the driving of brushless motors.
An example of this methodology is described in U.S. Pat. No. 5,969,491, assigned to STMicroeletronics, Srl, and incorporated herein by reference, in which the windings of the motor are put in a high impedance state for a brief period of time near the ZC occurrence to be detected.
The signal obtained is used as a reference for the measurement of the position and speed of the rotor.
The weak point of such an implementation is given by the fact that such a signal can be affected by electrical noise sources due both to circuit portions which are synchronous with the system for driving the motor, which are generally easier to mask, and to asynchronous circuit portions, which are more difficult to eliminate.
Some of the analog solutions proposed in the prior art provide the insertion of a low-pass filter inputting into the detection circuit of the ZC signal, for example as shown in FIG. 1 with reference to the “Bemf comparator” circuit which should be considered as associated with a filtering block.
The technical problem underlying the present invention is that of devising a new method for detecting the angular position of a rotor in an brushless electric motor, having such characteristics as to allow a correct identification of the back electromotive force (Bemf) ZC signal, avoiding the use of analog filters and improving costs and performance of the motor with respect to prior art solutions.